There are theme cruisers of ALL kinds, and I am sure they will only get more popular for several reasons:

(1) ships are ultra convenient for exhibition companies; they already hotel, theater and food facilities. All these facilities are in very close proximity.
(for more on this go to http://seasite.com, the home of Landry & Kling)

(2) it is way to add value to a cruise (and hence charge more for the same cruise)